In an air-conditioning apparatus in related-art, such as a multi-air-conditioning apparatus for a building, a refrigerant is circulated, for example, between an outdoor unit, as a heat source unit disposed outside of a structure and an indoor unit disposed inside of the structure. The refrigerant transfers or removes heat in order to heat or cool air, thus heating or cooling a space to be conditioned with the heated or cooled air. As the refrigerant used in such an air-conditioning apparatus, for example, an HFC (hydrofluorocarbon) refrigerant is often used. An air-conditioning apparatus has also been developed which uses a natural refrigerant, such as carbon dioxide (CO2).
In an air-conditioning apparatus called a chiller, cooling energy or heating energy is produced in a heat source unit disposed outside of a structure. Water, antifreeze, or the like is heated or cooled by a heat exchanger disposed in an outdoor unit, and conveyed to an indoor unit, such as a fan coil unit or a panel heater. And thereby, heating or cooling is performed (refer to Patent Literature 1, for example).
An air-conditioning apparatus called a heat recovery chiller is constituted such that a heat source unit is connected to each indoor unit by four water pipes arranged therebetween and, cooled water and heated water and the like are simultaneously supplied so that cooling or heating can be freely selected in indoor units (refer to Patent Literature 2, for example).
Further, an air-conditioning apparatus has been developed in which a heat exchanger for a primary refrigerant and a secondary refrigerant is disposed near each indoor unit to convey the secondary refrigerant to the indoor units (refer to Patent Literature 3, for example).
Furthermore, an air-conditioning apparatus has also been developed which is constituted such that an outdoor unit is connected to each branch unit including a heat exchanger by two pipes to convey a secondary refrigerant to an indoor unit (refer to Patent Literature 4, for example).
Moreover, air-conditioning apparatuses, such as a multi-air-conditioning apparatus for a building, include an air-conditioning apparatus in which a refrigerant is circulated from an outdoor unit to a relay unit and a heat medium, such as water, is circulated from the relay unit to each indoor unit to reduce conveyance power for the heat medium while circulating the heat medium, such as water, through the indoor unit (refer to Patent Literature 5, for example).